Four circular windows, each of radius $28cm$ are to be fitted with glass. Calculate the cost of glass at the rate of $Rs.4.25$ per $m^2.$

The correct option is A: $Rs.4.20$

Radius of a circular window, $r=28cm=\frac{28}{100}m$

Area of one circular window $=\frac{22}{7}\times r^2=\frac{22}{7}\times {\left(\frac{28}{100}\right)}^2{m}^2$

So, Cost of $1m^2$ glass $=Rs.4.25$

Hence, Total cost of glass (four circular windows) $=4\times 4.25\times \frac{22}{7}\times {\left(\frac{28}{100}\right)}^2$

$=4\times 4.25\times \frac{22}{7}\times \left(\frac{28}{100}\right)\times \left(\frac{28}{100}\right)$

$=4\times 4.25\times \frac{22}{1}\times \left(\frac{4}{100}\right)\times \left(\frac{28}{100}\right)$

$=\frac{4\times 4.25\times 22\times 4\times 28}{10000}$

$=Rs.4.18\sim Rs.4.20$